Lactate dehydrogenase isoenzymes in cerebrospinal fluid were measured during the first 24 h of life in 25 asphyctic neonates. The infants were subjected to clinical and developmental examinations for a mean follow-up period of 15.2 months. The mean values for cerebrospinal LDH2(MH3) and LDH3(M2H2) isoenzymes were significantly higher in asphyctic infants who died from hypoxic-ischemic encephalopathy or who survived but suffered neurologic sequelae, than they were in those asphyctic infants who survived and were normal in the follow-up studies. Therefore, the authors conclude that the lactate dehydrogenase isoenzyme pattern in cerebrospinal fluid may be of value when assessing anoxic brain damage.